Organic Cocrystals of TCNQ and TCNB Based on an Orthocetamol Backbone Solved by Three-Dimensional Electron Diffraction

We report the first cocrystals of TCNQ and TCNB based on orthocetamol, a regioisomer of paracetamol. Through a simple solution growth process, cocrystals were produced containing orthocetamol as electron donors with coformers of either 7,7,8,8-tetracyanoquinodimethane (TCNQ) or 1,2,4,5-tetracyanobenzene (TCNB), as electron acceptors. Because of submicron crystalline domains, 3D electron diffraction was employed for structure solution in both systems. This revealed that both systems crystallize in a 1:1 stoichiometry in which orthocetamol forms a backbone allowing for linking of acceptor molecules in a mixed-stack configuration. Orthocetamol-TCNQ adopts an noncentrosymmetric Pc symmetry, and orthocetamol-TCNB a centrosymmetric P-1 symmetry. UV-vis and FT-IR were employed to probe the ability of these cocrystals to create charge transfer (CT) systems, revealing a low degree of charge transfer. Still, the possibility to use orthocetamol backbone as structural scaffold paves the way for an entirely new class of CT materials.